Hand-held, power driven hedge trimmers having an extended cutting blade portion are well knowwn. Probably the commonest of these is the electrically powered hedge trimmer provided with an extension cord that is readily plugged into a household electrical socket. The basic structure of such device is designed to reduce the weight and provide a balanced and comfortable grip by a user operating the same to cut or sculpt bushes or hedgerows. Such cut material mostly comprises relatively soft stems, and, occasionally, woody stems that require a significant amount of force to sever them. Basically, therefore, hedge trimmers of the sort to which this invention relates are intended to be light, versatile pieces of hand-held equipment operable in a variety of orientations and capable of trimming vegetation without unduly tiring out a user.
The conversion of rotary motion into reciprocating motion, between cooperating cutting blades to cut grass, is long known, as exemplified in U.S. Pat. No. 51,746, to Palmer. This device has ground-contacting wheels of a lawnmower, each formed withan internal orbital gear of relatively large diameter in engagement through a double gear train to a crank mechanism for reciprocating cutting blades through a crank device. A somewhat comparable device is disclosed in Reissued U.S. Pat. No. 3394, to Crook, in which ground-engaging lawnmower wheels are formed to provide an internal orbit gear engaged through a gear train to generate speeded-up reciprocating motion through a crank to operate grass-cutting blades. In both examples, however, it is the outer orbital gear that is powered by motion of the entire device in contact with the ground, the gears are all essentially exposed to dirt and the elements, and the reciprocating motion is relatively speeded up as compared to the speed of rotation of the ground contacting wheels. Also, in both examples, reciprocating motion is generated by a rotary crank element.
U.S. Pat. No. 1,594,244, to Daniels, discloses a device in which the gears and crank mechanism are totally enclosed with lubricant to protect the same, while providing a reciprocating motion to cutting blades in a harvesting machine. In this device, a ring-type orbital gear engages a rotating planet gear rotatably carried on a crank driven by a power source. The rotating planetary wheel has attached to it a crank engaged to an element to be reciprocated. The device produces reciprocating motion because the gear wheel has an effective diameter exactly half that of the engaging orbital gear.
In U.S. Pat. No. 1,512,781, to Masland, a high-speed surgical saw is disclosed in which a rotary power input drive provided with a sinuous peripheral groove serves as a cam engaging a pin-like element attached to a reciprocating blade-holding element. The device of Masland is obviously intended to provide a short stroke, high-speed, reciprocating motion to a fine-toothed surgical sawblade and does not include any speed-reduction gearing. Obviously, such a device must be light and fairly small to afford the surgeon the necessary facility for cutting through a variety of tissues without exerting undue force.
U.S. Pat. No. 1,763,500, to Bowen, discloses an electrically powered sabre saw device in which an electrically powered motor provides a high-speed input, geared down through two pairs of spur gears to rotate a relatively solid drum provided with a fairly long travel groove on its outer periphery. This groove engages a pin-like portion of an element constrained to reciprocate back and forth with respect to the case while carrying at one end a straight, toothed sawblade. Unlike the device of Masland, the sabre saw of Bowen is designed to provide a relatively low-spped high force output, with a fairly long throw, so that the blade may cut through wood of some thickness. Also, presumably because wooden knots may be encounted for cutting, the grooved drum is solid and has a relatively high inertia to prevent stalling of the blade. In both Masland and Bowen, the groove and the pin engaged thereby are enclosed and may be lubricated in a manner that excludes extraneous dirt.
U.S. Pat. No. 2,633,636, to Szostek, discloses an electric hedge trimmer in which a rotary motor, through an enclosed set of five spur gear pairs, drives a solid rotating cylindrical element provided with two oppositely oriented continuous grooves to serve as cams. The grooves respectively engage a pin-like element of each of two adjacently placed reciprocating cutting elements formed with cutting teeth. This apparatus is provided with two side-by-side handles symmetrically disposed about the drive motor and provided with a flat guide element 11 parallel to the cutting teeth.
None of the devices described hereinabove, which are fairly typical of the prior art, combine speed reduction, light weight and durability and none provides insulation for the operator from inevitable and fatiguing vibration generated during operation of the device. There is, therefore, a definite need for a sturdy but light, hand-held, power driven hedge trimmer in which unpleasant feedback of vibrations to the user is minimized.
Hand-held, power-driven hedge trimmers of known type generally have a hand-held portion with handles and guard elements, containing a vertically oriented drive motor and/or gear and cam elements, and a forwardly extending cutting blade portion. the cutting blade portion includes a generally planar form that has a blade support element, a blade retaining element spaced therefrom, and a reciprocating cutting blade element contained and guided therebetween to coact with at least the support blade element to generate cutting action by reciprocatory motion relative thereto. These structures typically include a transverse elongated slot in a movable cutting blade element, for engaging a downwardly dependent pin powered by the drive motor to rotate in the plane of the cutting blade element.
Among the problems encountered in the hitherto described prior art device are the following: cutting with a vertically oriented drive motor and gearing causes the hand-held portion to be unwieldy; the coaction of the pin rotating around the vertical axis and engaging the reciprocating cutting blade element as well as cutting of though stems generates undesirable vibrations and causes fatigue to the user; and, over a period of time, there is unacceptably high wear in the elongate slot that engages the downwardly depending pin driving the same.
The present invention is intended to alleviate all of the problems discussed above.